When an electric device such as a power conversion device passes or receives power to or from a power supply, in an inductor component such as a reactor provided in the electric device, temperature increase occurs in accordance with conduction loss caused by the winding resistance and flowing current of the inductor component. In order to suppress excessive temperature increase in the inductor component, the size of the inductor component itself may be increased. However, a space for placing the increased-size inductor component is needed. Accordingly, in order to suppress excessive temperature increase in the inductor component while avoiding size increase in the inductor component, control is used in which, while the temperature of the inductor component is acquired, operation control of the electric device is adjusted to decrease flowing current of the inductor component.
While the temperature of the inductor component changes in accordance with conduction loss due to flowing current as described above, the temperature change at this time is accompanied with a lag period specific to the inductor component. That is, after the flowing current increases, time lag occurs until the temperature of the inductor component itself increases. In the control in which operation control of the electric device is adjusted after the temperature of the inductor component is actually measured using a temperature measurement device and temperature increase is detected, it takes time until the temperature of the inductor component decreases, and thus there is a possibility that the permissible temperature is exceeded. Therefore, in order to accurately obtain the temperature of the inductor component which changes with a lag period relative to change in the flowing current without using a measurement device, technology in which the temperature of the inductor component at a predetermined time is estimated is disclosed as shown below.
A current detection unit detects the current value of AC current flowing in accordance with a load. A temperature prediction unit predicts the temperature of a predetermined part in an optional operation continuation period on the basis of information during operation and the current value detected by the current detection unit. A temperature θtn of a predetermined part at a predetermined time tn is calculated using the following expression.θtn=θt(n−1)+(sat1−θt(n−1))×[1−EXP(−(tn−t(n−1))/τ1]−(reference temperature−ambient temperature)Whereθsat1=I×I×K1
θtn: temperature of predetermined part at time tn
θt(n−1): temperature of predetermined part at time t(n−1)
θsat1: saturation temperature
I: current value of AC current flowing in accordance with load
K1: coefficient during operation of power conversion unit
τ1: thermal time constant during operation of power conversion unit
Reference temperature: ambient temperature around power conversion device when operation test for power conversion device was performed in advance
Ambient temperature: ambient temperature around power conversion device as product
By substituting the present current value into I, substituting an operation start time of the power conversion unit into t(n−1), substituting the present time into tn, and substituting the reference temperature into θt(n−1), the temperature of the predetermined part at present can be calculated.
In addition, by substituting the present current value into I, substituting the present time into t(n− 1), substituting a desired time after the present (in the future) into tn, and substituting the temperature of the predetermined part at present into θt(n− 1), the temperature of the predetermined part at the desired time can be calculated.
In addition, a power conversion device including the temperature prediction unit outputs an instruction about heat resistance protection for the inductor component on the basis of the temperature of the inductor component predicted as described above (see, for example, Patent Document 1).